US 2004072668 describes a centrifugal separator having a casing with a nozzle provided in the casing side. Above the casing, i.e. closer the longitudinal axis, a weir may be provided. The depth of a pool of liquid in the bowl is determined by the diameter of the nozzle provided that the rate of feed to the separator is constant.
U.S. Pat. No. 7,022,061 describes a centrifugal separator that includes a liquid phase discharge port having a tubular member with an elbow bend.
U.S. Pat. No. 4,575,370 discloses a centrifugal separator having a bowl with a base plate and liquid phase outlet openings provided in said base plate. The outlet openings are partly covered by weir plates to adjust the level of liquid or depth of a pool of liquid in the bowl. Generally, the use of a weir ensures that the level of liquid in the bowl substantially cannot exceed the level of the weir, because the area of the opening above the weir from a practical view is unlimited. According to U.S. Pat. No. 4,575,370 a notch is provided in the overflow edge of the weir or a through hole is provided in the weir to make it possible, in a start-up phase of running the separator, to obtain operation with a lower liquid level at a smaller rate of feed to the separator.
A problem in such a centrifugal separator is that liquid flowing over the overflow edge of the weir plate tends to cling to the outside of the base plate thereby being accelerated which is energy consuming thus causing energy loss and therefore an extra power consumption of up to 15%. Further, on entry into the bowl the feed is accelerated to a rotational speed and the energy thus consumed is lost when the liquid phase exits over a weir at the outlets in the base plate.
The separator of the above-mentioned US 2004072668 seeks to solve this problem. However the use of a nozzle with a given diameter entails that at a varying feed rate the level of liquid in the bowl will also vary.